Most plants have specialized hair-like trichome structures on leaf surfaces, non-glandular trichomes being very common, glandular trichomes being less common. Glandular trichomes are capable of storing relatively large amounts of secondary metabolites, like terpenoids, as part of the essential oil of the plant, making them a target for the production of valuable small molecules.
For example, peppermint oil, consisting primarily of monoterpenes and minor quantities of sesquiterpenes is synthesized and accumulated in specialized peltate glandular trichomes of the peppermint plant and finds use as a flavor in numerous consumer products (e.g., chewing gum, mouthwash . . . ) in the confectionary and pharmaceutical industries.
Whereas since the distant past, 8000 B.C. up the present, Cannabis in various forms was either eaten or smoked, the major usage being a recreational drug all over the world, cannabinoids and their derivatives were the mainstay of early medicine and the seeds were integrated into most every cuisine around the world, Cannabis products have been consumed in various forms for thousands of years. Descriptions of medical uses in Chinese texts date from the first century A.D., disclosing oral consumption in herbal tea concoctions, used for pain relieving and sleep inducing. The use of cannabis in Hindu India was largely popularized by Shiva smoking the leaf or resin extracts for their psychoactive properties. The use was spread through Arab lands in the Middle Ages, before coming into Europe and the Americas. For centuries, Cannabis resin was made by hand rubbing the flowers or sifting with fine cloths as screens.
Cannabinoids are receiving just recently a new and increasing interest again for recreational freedom, State taxes, nutrition and pharmaceutical commercial and industrial purposes.
Glandular trichomes of the Cannabis Sativa plant store amounts of cannabinoids, in particular tetrahydrocannabinol (THC) and cannabidol (CBD). Almost all current research focuses either on genetically engineered plants exhibiting enhanced contents of THC, CBD or other molecules, or on medical applications of particular cannabinoids. The known extraction methods are usually dedicated to isolate a specific molecule and thus involve a solvent. For example, US 2013/0079531 (to Barringer) teaches an EtOH extraction at −20° C.
There is to our knowledge very few methods to purify integer glandular trichomes.
U.S. Pat. No. 6,158,591 (to Delp) uses cold water and ice in a wash process to cause the resins to become brittle, while the remaining plant material becomes more flexible. Separation is accomplished using an extractor having a washing chamber and a screen filter disposed above a settling chamber. A collection bottle is placed below, and may include a filter to separate resin particles from the solute. A corresponding device comprising two sieving bags of different mesh size for separating resin particles from various plant material may be found for example under the name of “Ice-O-Later®”.
A drawback of the ice-water methods is that some components of the resin material are lost by dissolution in the water. Another drawback of these methods is that the resin must be quickly and carefully dried thereafter to avoid deterioration by fungal growth under moisture. These drawbacks may lead to an alteration of organoleptic properties of the resin.
A dry process is know from the publication of Yerger et al, Plant Physiology, 1992, 99, 1-7, wherein deep frozen plant material are placed together with crushed dry ice (CO2) in a vortex mixer. Glandular trichomes are then separated by sieving. This paper teaches that the dry ice particles act mechanically to separate trichomes from pedicels. Corresponding device may be commercially available under the name of “Pollinator®”. Such device comprises a sifting drum accommodating the plant material, tumbling inside a casing, so that the finer fraction of particles fall through the screen around the drum onto the bottom of the casing for later collection. The process is extremely sensitive to the operating parameters such as the temperature, the humidity and the process duration. A very cold and dry atmosphere is required, and short processing time is necessary to recover the resin with a higher purity. Under these conditions, the yield is low.